Magnetrons

ABSTRACT

In a magnetron device of the class comprising a magnetron tube, permanent magnets on radially opposite sides of the magnetron tube yoke means for applying a magnetic field across the magnetron tube, and cooling means surrounding the magnetron tube and at least a portion of the permanent magnets, the widths of the permanent magnets being gradually decreased toward the magnetron tube thus forming tapered side surfaces.

United States Patent 1 [111 3,716,750

Nakada et al. [451 Feb. 13, 1973 54] MAGNETRONS 3,493,8l0 2 1970 Valles ....315 39.71 x

3,562,579 2/1971 Kakizawa ..3l5/39.7l Inventors: Kusuo Nakada, Tmmkats 8"" 3,454,824 7/1969 Owaki et al. ..315/39.71 Assigneez Hitachi, Ltd. Tokyo, J p 2,765,425 10/1956 Mlllman ..3l5/39.65 both of Mobara'shlJapan Primary Examiner-Herman Karl Saalbach [22] Filed: May 12, 1971 Assistant ExaminerSaxfield Chatmon, Jr. pp No.2 142,641 Attorney-Cra1g, Antonelll & Hill Foreign Application Priority Data [57] ABSTRACT In a magnetron device of the class comprising a mag- May 30, 1970 Japan ..45/46034 netron tube permanent magnets on radially pp sides of the magnetron tube yoke means for applying a [52] U.S. Cl. ..3l5/39.7l, 313/157, 313/46, magnetic field across the magnetron tube and cooling 315/3951 means surrounding the magnetron tube and at least a I "H011 portion of the permanent magnets the of the Fleld Search-3153951, 3953, 39-71, permanent magnets being gradually decreased toward 46 the magnetron tube thus forming tapered side surfaces. [56] References Cited 9 Claims, 6 Drawing Figures UNITED STATES PATENTS 3,588,588 6/l97l Numata ..315/39.7l

PATENTEUFEWQ 3,716,750

SHEET 10F 2 INVENTORS KUSUO NAKADA AND TOMOKATSU OGUR ig, Anl'oneui w H-LZL ATTORNEYS PATENTEDFEBI31975 3,716,750

SHEET 2 OF 2 F164 A m wmw INVENTORS KUSUO [\AKADA AND TOMOKATSU oeuRo BY Craig, Anloneui '4' ATTORNEYS MAGNETRONS BACKGROUND OF THE INVENTION This invention relates to a magnetron device, and more particularly, to a magnetron device utilizing permanent magnet means disposed radially on either side of an evacuated magnetron tube having a generally cylindrical shape.

The prior art magnetron device of this type generally comprises an evacuated magnetron tube, a pair of permanent magnets disposed on radially opposite sides and the axis of the permanent magnets being coincident with a plane passing through the longitudinal axis of the magnetron tube and yokes interconnecting the magnets for applying an intense magnetic field to the magnetron tube. When designing the permanent magnets utilized to apply a field of a predetermined intensity to the interaction space in the magnetron tube, it is necessary to take into account the value of the leakage flux passing through the space between the yokes. To compensate for a large amount of leakage flux, it is necessary to increase the cross-sectional area and the height of the permanent magnets, thus requiring bulky magnets. For this reason, in order to use small magnets which can apply a field of predetermined intensity to the interaction space in the magnetron tube with only a small amount of leakage flux, it is necessary to dispose the magnets as close as possible to the magnetron tube.

Further, as is well known in the art, the magnetron tube generates a large quantity of heat during its operation. Such a large quantity of heat not only lowers the vacuum in the magnetron tube but also adversely affects the magnetic characteristics of the permanent magnets disposed in the neighborhood of the tube. Especially, when the permanent magnets comprise sintered ferrite magnets, the deterioration of their magnetic characteristic is so excessive as to affect the operating characteristics of the magnetron. For this reason, it is the practice to surround the magnetron tube with heat dissipating means for efficiently dissipating the heat generated during the operation thereof. However, close disposition of the permanent magnets to the magnetron tube renders it impossible to provide the heat dissipating means in the region in which the magnets are to be disposed; whereby, the construction of the heat dissipating means is limited, thus decreasing the efficiency of heat dissipation.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a new and improved magnetron device utilizing permanent magnet means so constructed that close disposition thereof to the magnetron tube does not affect the heat dissipating efficiency.

Another object of this invention is to provide an improved magnetron device wherein a magnetron tube is disposed in a magnetic circuit comprising permanent magnets and yokes without increasing the leakage flux.

Still another object of this invention is to provide a novel magnetron device utilizing a small permanent magnet which is capable of generating a field of the required intensity for the magnetron tube.

A further object of this invention is to provide an improved magnetron of small size and light weight, including means for efficiently dissipating heat therein.

According to this invention, there is provided a mag netron device of the class comprising a magnetron tube, permanent magnet means disposed in parallel to the magnetron tube for applying a magnetic flux across the magnetron tube and cooling means surrounding the magnetron tube, and at least a portion of the permanent magnet means being characterized in that the widths of the permanent magnets are gradually decreased toward the magnetron tube, thus forming tapered side surfaces. This construction not only decreases the leakage flux, but also assures adequate cooling of the magnetron tube as well as the permanent magnet means.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects and advantages of the invention will be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a front elevation of one embodiment of the magnetron in accordance with the invention;

FIG. 2 shows a cross-sectional view of the magnetron shown in FIG. 1, taken along Line IIII;

FIG. 3 shows a diagram illustrating the relationship between the magnetron tube and the permanent magnet constructed according to the teachings of the invention;

FIGS. 4 and S are diagrammatic representations showing the relationship between the cross-sectional configurations of the magnetron tube and the permanent magnet; and

FIG. 6 shows a cross-sectional view of a modified embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the accompanying drawing, FIGS. 1 and 2 illustrate a preferred embodiment of this invention in the form of a magnetron device utilizing radial fins as the heat dissipating means for the magnetron tube. The magnetron shown therein comprises an evacuated magnetron tube or envelope 1, an insulator bushing 2 of ceramic or glass, for example, for housing an output terminal lead 3, permanent magnets 4 and 5 with their pole faces S and N interconnected with the magnetron tube 1 by magnetic yokes 6 and 7, heat dissipating or cooling fins 8 radially extending about the longitudinal axis of the magnetron tube 1 and a duct 9 for passing cooling air along the surface of the cooling fins. With the magnetron device of the construction just described the cooling air flows in the axial direction of the magnetron tube. The front elevation shown in FIG. 1 is not different from that of the conventional magnetron; however, the cross-sectional view of FIG. 2 clearly shows the novel relationship between the magnetron tube and the permanent magnets as well as the novel cross-sectional shape of the permanent magnets.

As shown, the magnetron tube 1 comprises a cathode electrode 11 and an anode electrode 12 concentric with the cathode electrode, and including a plurality of vanes 13 radially protruding toward the cathode electrode for defining a plurality of resonant cavities. Between the cathode electrode and the anode vanes is defined a cylindrical interaction space 14 in which the magnetic field created by the flux generated by the two permanent magnets 4 and flowing through the 5 and yokes 6 and 7 coacts with the electron current flowing from cathode electrode 11 to anode vanes 13. This construction of the magnetron tube 1 has been well known in the art.

According to the invention, the permanent magnets 4 and 5 are disposed on the radially opposite sides of and in parallel with the magnetron tube 1 and are positioned as close as possible to the magnetron tube. The invention is characterized in that the width of the inner side walls 41 and 51 of the permanent magnets confronting the peripheral wall of the magnetron tube is a minimum and the width of the magnets gradually increases from these inner side walls toward the outside, and that the direction of the tapered surfaces 42 and 52 substantially coincides with that of the radial cooling fins 8.

The relationship between the magnetron tube and the permanent magnets can be more fully appreciated from FIG. 3. Assuming a permanent magnet whose cross-section can be shown by a rectangle 43, the inside corners of the magnet are cut away along straight lines 1 and 1 that extend radially outwardly from the center 0 of the magnetron tube 1, thus forming a permanent magnet 4 of a configuration shown in FIG. 2. The quantity of flux generated by permanent magnet 4 having such tapered cuts is conducive to the efficient operation of the magnetron. Such a permanent magnet with tapered cuts is equivalent to a rectangular permanent magnet 44 having the same axial length and the same contains sectional area as depicted by the dot and dash lines in FIG. 3. If the magnet 4 and the equivalent magnet 44 were made of the same material, they would produce the same quantity of magnetic flux, thus applying to the magnetron tube magnetic fields of the same intensity. In the case of the magnet with tapered cuts, it is possible to provide the heat dissipating means in regions to the left of radial lines I, and 1 whereas, in the case of the equivalent magnet 44 of rectangular section, regions in which the heat dissipating means can be disposed are limited by the corners 45 of the magnet, or to the left of radial lines 1 and 1 passing through corners 45. In the case shown in FIG. 3, the ratio of angle A subtended by line 1 and the normal line through the center 0 of the magnetron and angle B subtended by line and the normal line through the center is equal to 1.4, which indicates a corresponding increase in the heat dissipation.

FIG. 4 shows a modified embodiment of the invention wherein permanent magnet 4 is formed by cutting off portions of a cylindrical block along radial lines I and 1,, thus providing tapered side surfaces.

In another embodiment shown in FIG. 5, the permanent magnet 4 is formed by cutting an annulus of magnetic material along radial lines 1 and 1 In any case, the body of the permanent magnet may have any desired sectional configuration before it is cutinto a permanent magnet 4 along radial lines passing through the center 0 of the magnetron tube; for example, it may have the shape of an oval.

As above described, since in accordance with this invention, the permanent magnets are disposed as close as possible to the magnetron tube for the purpose of decreasing the leakage of the flux passing through the space between the yokes on the way from the permanent magnets to the magnetron tube, it is possible to decrease the size of the permanent magnets by an amount corresponding to the decrease in the leakage flux. Further, tapered inner ends of the pole pieces of the magnets eliminate the limitation of the regions in which the heat dissipating means can be arranged imposed by the close disposition of the magnets to the magnetron tube, whereby the high heat dissipation efficiency of the prior design can be preserved.

Although in the foregoing embodiment, the invention has been applied to magnetrons of the type wherein the heat dissipating means comprise radial fins and wherein the cooling air flows in the axial direction of the magnetron tube, it should be understood that the invention is by no means limited to the particular type. Thus, for example, a plurality of axially spaced apart parallel flat cooling fins 10 may be provided perpendicular to the longitudinal axis of the magnetron tube for transferring heat to the cooling air flowing in transverse direction to the magnetron tube axis passing between the fins.

While we have shown and described several embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to a person skilled in the art, and we therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are obvious to one of ordinary skill in the art.

What is claimed is:

1. A magnetron device comprising an evacuated magnetron tube of generally cylindrical configuration, a pair of permanent magnets disposed in close relationship to and extending along the sides of said magnetron tube radially opposite to each other, the widths of said permanent magnets confronting the magnetron tube gradually decreasing toward the axis of said magnetron tube, thus forming tapered side surfaces on said permanent magnets, magnetic yoke means interconnecting the common ends of said permanent magnets for applying a magnetic field to said magnetron tube, and cooling means surrounding said magnetron tube and at least a portion of said tapered side surfaces of said permanent magnets for conveying heat therefrom.

2. The magnetron device according to claim 1 wherein said tapered side surfaces extend in the radial direction with respect to the axis of said magnetron tube.

3. The magnetron device according to claim 1, wherein said cooling means comprises a plurality of cooling fins radially extending from said magnetron tube, said tapered side surfaces coextending with said cooling fins.

4. The magnetron device according to claim 1, wherein said cooling means comprises a plurality of spaced apart parallel flat fins disposed at substantially perpendicular to the axis of said magnetron tube.

5. The magnetron device according to claim 1, wherein the inner end walls of said permanent magnet confronting said magnetron tube are flat.

6. The magnetron device according to claim 2, wherein said cooling means comprises a plurality of cooling fins radially extending from said magnetron tube, said tapered side surfaces coextending with said cooling fins.

7. The magnetron device according to claim 2, wherein said cooling means comprises a plurality of spaced apart parallel flat fins disposed at substantially perpendicular to the axis of said magnetron tube.

8. A magnetron device comprising an evacuated magnetron tube having a generally cylindrical configuration, a pair of permanent ferrite magnets disposed in close relationship to and extending along the sides of said magnetron tube on radially opposite sides thereof, the widths of said permanent magnets confronting the magnetron tube gradually decreasing toward said magnetron tube, thus forming tapered side surfaces on said permanent magnets, magnetic yoke means interconnecting said permanent magnets for applying a magnetic field to said magnetron tube, and cooling means surrounding said magnetron tube and at least a portion of said tapered side surfaces of said permanent magnets for conveying heat therefrom, said means comprising a plurality of cooling fins extending radially from said magnetron tube and said tapered side surfaces of said magnets coextending with said cooling fins.

9. A magnetron device comprising an evacuated magnetron tube having a generally cylindrical configuration, a pair of permanent ferrite magnets disposed in close relationship to and in parallel with said magnetron tube on radially opposite sides thereof, the widths of said permanent magnets confronting the magnetron tube gradually decreasing toward said magnetron tube, thus forming tapered side surfaces on said permanent magnets which extend in the radial direction with respect to the axis of said magnetron tube, magnetic yoke means interconnecting said permanent magnets for applying a magnetic field to said magnetron tube, and cooling means surrounding said magnetron tube and at least a portion of said tapered side surfaces of said permanent magnets for conveying heat therefrom, said means comprising a plurality of cooling fins extending radially from said magnetron tube and said tapered side surfaces of said magnets coextending with said cooling fins. 

1. A magnetron device comprising an evacuated magnetron tube of generally cylindrical configuration, a pair of permanent magnets disposed in close relationship to and extending along the sides of said magnetron tube radially opposite to each other, the widths of said permanent magnets confronting the magnetron tube gradually decreasing toward the axis of said magnetron tube, thus forming tapered side surfaces on said permanent magnets, magnetic yoke means interconnecting the common ends of said permanent magnets for applying a magnetic field to said magnetron tube, and cooling means surrounding said magnetron tube and at least a portion of said tapered side surfaces of said permanent magnets for conveying heat therefrom.
 1. A magnetron device comprising an evacuated magnetron tube of generally cylindrical configuration, a pair of permanent magnets disposed in close relationship to and extending along the sides of said magnetron tube radially opposite to each other, the widths of said permanent magnets confronting the magnetron tube gradually decreasing toward the axis of said magnetron tube, thus forming tapered side surfaces on said permanent magnets, magnetic yoke means interconnecting the common ends of said permanent magnets for applying a magnetic field to said magnetron tube, and cooling means surrounding said magnetron tube and at least a portion of said tapered side surfaces of said permanent magnets for conveying heat therefrom.
 2. The magnetron device according to claim 1 wherein said tapered side surfaces extend in the radial direction with respect to the axis of said magnetron tube.
 3. The magnetron device according to claim 1, wherein said cooling means comprises a plurality of cooling fins radially extending from said magnetron tube, said tapered side surfaces coextending with said cooling fins.
 4. The magnetron device according to claim 1, wherein said cooling means comprises a plurality of spaced apart parallel flat fins disposed at substantially perpendicular to the axis of said magnetron tube.
 5. The magnetron device according to claim 1, wherein the inner end walls of said permanent magnet confronting said magnetron tube are flat.
 6. The magnetron device according to claim 2, wherein said cooling means comprises a plurality of cooling fins radially extending from said magnetron tube, said tapered side surfaces coextending with said cooling fins.
 7. The magnetron device according to claim 2, wherein said cooling means comprises a plurality of spaced apart parallel flat fins disposed at substantially perpendicular to the axis of said magnetron tube.
 8. A magnetron device comprising an evacuated magnetron tube having a generally cylindrical configuration, a pair of permanent ferrite magnets disposed in close relationship to and extending along the sides of said magnetron tube on radially opposite sides thereof, the widths of said permanent magnets confronting the magnetron tube gradually decreasing toward said magnetron tube, thus forming tapered side surfaces on said permanent magnets, magnetic yoke means interconnecting said permanent magnets for applying a magnetic field to said magnetron tube, and cooling means surrounding said magnetron tube and at least a portion of said tapered side surfaces of said permanent magnets for conveying heat therefrom, said means comprising a plurality of cooling fins extending radially from said magnetron tube and said tapered side surfaces of said magnets coextending with said cooling fins. 